The Wordy Warrior covers a well-traveled subject in an interesting way in her latest post. We've already talked in-depth about how to get into a good raiding guild (and we've even covered some amazing guild applications), but straight from the trenches of guild leadership, Ariedan sends an open letter to anyone applying to her guild with, some might say, the wrong attitude.
Here's the thing: especially if you're applying to a progression guild, odds are that they don't need you. They're progressing just fine, and bringing you in just opens the door for more drama. It's a risk, and it's your job to convince them to take that risk, hopefully for the benefit of both. So if you show up to an application and don't take it seriously, and flip out when they question your background, and expect them to take you on without any proof you'd be valuable to them, don't be surprised when they laugh you right out of their forums.
We're probably preaching to the choir here -- if you're reading this site, you probably already have at least one clue, and are either in a guild you like that is not a raiding guild, or are in a progression guild that you got into because you were able to justify that risk. But if you're still having trouble figuring out how to get where you want to be, take WW's advice to heart: it's on you to justify your entry to the guild, it's not on them to put up with you.